sleeving versus stroking....

[bigtoe01]

Long and thin should be more efficient, also less pressure to cause (inevitable) piston bounce, hence a lighter piston can be used, which moves faster, less recoil etc. I've high hopes of 23mm

I thought it would have had a higher peak pressure earlier so more susceptible to bounce due to smaller pressure cylinder diameter....we shall soon see, if i get a chance I will swap one of the triggers from one of my 80's (they all have rotating pistons so modified trigger sears) into the 77 over the next 2 days with an LGV spring and see how it does.

Really hoping this works well, very keen on going 23mm in the LGU also if it does, aluminium2buy on the bay stocks 25mm od 1mm wall in short lengths. To date i have never been happy with the LGU, its a fine gun but not a patch on my TX now, if the 77 is transformed with this 23mm conversion it will just have to happen in the LGU also along with a new trigger blade.

[NickG]

I thought it would have had a higher peak pressure earlier so more susceptible to bounce due to smaller pressure cylinder diameter....we shall soon see, if i get a chance I will swap one of the triggers from one of my 80's (they all have rotating pistons so modified trigger sears) into the 77 over the next 2 days with an LGV spring and see how it does.

Really hoping this works well, very keen on going 23mm in the LGU also if it does, aluminium2buy on the bay stocks 25mm od 1mm wall in short lengths. To date i have never been happy with the LGU, its a fine gun but not a patch on my TX now, if the 77 is transformed with this 23mm conversion it will just have to happen in the LGU also along with a new trigger blade.

I am not impressed with the lgu either, I think the firing cycle is far too slow, I am going to short stroke mine with a simple head extension, and maybe a snappier spring, and yes you guessed it I will be using an o ring, though I am very impressed with the shot feel of the new hw seal.

[bigtoe01]

I am not impressed with the lgu either, I think the firing cycle is far too slow, I am going to short stroke mine with a simple head extension, and maybe a snappier spring, and yes you guessed it I will be using an o ring, though I am very impressed with the shot feel of the new hw seal.

I went the other way, i managed to pick up an early 7.5j LGV piston, which is modular, so I was able to shorten the rod and push back to 80mm stroke keeping maximum spring room. I wish I could find a source of true 7.5j pistons as they work beautifully in Diana rifles also.
One area I partially looked at (thinking about it now) is piston weight, i should push it down more as i now favour 200g where the LGU is at 230g right now. There is a possibility this is all I will need to do, although im kinda hoping 23mm is the way forward.

Annoys me we can only buy the 16j piston service kits, i would probably buy 2x more 7.5j kits than the 16, i have already worked thru over 50 16j kits now.

[NickG]

I went the other way, i managed to pick up an early 7.5j LGV piston, which is modular, so I was able to shorten the rod and push back to 80mm stroke keeping maximum spring room. I wish I could find a source of true 7.5j pistons as they work beautifully in Diana rifles also.
One area I partially looked at (thinking about it now) is piston weight, i should push it down more as i now favour 200g where the LGU is at 230g right now. There is a possibility this is all I will need to do, although im kinda hoping 23mm is the way forward.

Annoys me we can only buy the 16j piston service kits, i would probably buy 2x more 7.5j kits than the 16, i have already worked thru over 50 16j kits now.

You obviously like those pistons !, I was also thinking lighter weight, along with the spring, got to watch cocking effort though.

I am only experimenting as there is no point in making it into a TX I already have two of those, I will probably move it along once I know what's going on with it

[bigtoe01]

You obviously like those pistons !, I was also thinking lighter weight, along with the spring, got to watch cocking effort though.

I am only experimenting as there is no point in making it into a TX I already have two of those, I will probably move it along once I know what's going on with it

My goal is to have all the following shooting just how i like them:
TX200 done
440TH done
LGU work in progress
77k done but now undone

In the end they will probably all shoot very similar, however they do still all have their own character too.

[Shed tuner]

One area I partially looked at (thinking about it now) is piston weight, i should push it down more as i now favour 200g where the LGU is at 230g right now.

I seem to remember having that argument with you 6 months or so ago... good to see we're all on the same page now

Looking forwards to trying that 23mm HW of yours, hopefully I'd have had time to do a 23mm TX by then

[bigtoe01]

I seem to remember having that argument with you 6 months or so ago... good to see we're all on the same page now

Looking forwards to trying that 23mm HW of yours, hopefully I'd have had time to do a 23mm TX by then

It could be even better if the piston was lighter weight..however with that comes increased cocking effort...i will see what its like here for an extended period first i think.

The LGU is up next for surgery..all depends on sleeve tube. The piston will just be reduced in dia, nose machined back and an alu nose screwed on with O ring...same spec as the 77. Only difference will be LGU has 3.5mm TP...will see if that helps or hinders.

[Shed tuner]

It could be even better if the piston was lighter weight..however with that comes increased cocking effort...i will see what its like here for an extended period first i think.

The LGU is up next for surgery..all depends on sleeve tube. The piston will just be reduced in dia, nose machined back and an alu nose screwed on with O ring...same spec as the 77. Only difference will be LGU has 3.5mm TP...will see if that helps or hinders.

All good For sure cocking effort vs more spring/lower piston weight is the trade off - kinda like driving a nail in - you can use a light hammer and hit with with all your might, or a heavy one and give it a moderate tap... Trouble is with airguns whilst there's no doubt the heavy piston is efficient at compressing air, moving an unnecessarily large hunk of metal around has some downsides. Nail bashing is simpler.

BTW Your peak pressure comment earlier - I think you are right, what I meant was that for a given pressure, the actual force decelerating the piston would obviously be less, as the surface area upon which it's acting would be reduced. I think that's what would enable a higher peak pressure to be achieved (as the piston would decelerate more slowly as the pressure built up).

Gotta try and do my 23mm TX conv this weekend... it's my birthday, so I may elect to celebrate by sodding off to the shed for the day

[NickG]

You have got me itching to give the 23mm a go, I have a tx comp tube, and I have a 97 comp tube , and I have hydraulic tubing that would lend itself to the job, trouble is my 77 stock is back at custom stocks being rectified, and the tx is the test bed for my buttoned ally piston, that's a dilemma